These studies focus on a longitudinal analysis of behavioral changes in affective illness, interrelating these observations with physiological and biological variables; emphasis is on circadian (24-hour) and longer rhythms. Results to date indicate that some regularly cycling bipolar patients show circadian desynchronization in temperature, so that the normal rhythm is no longer "locked in" to the environmental 24-hour day-night cycle, but tends to drift in and out of phase. Alterations in this cycle have been found not only naturalistically in some patients, but can be manipulated by such procedures as day-night reversal and artificial 21-hour days. A new ambulatory non-telemetric physiological monitor has been developed and tested in inpatients and outpatients. The relationship between biological rhythms and various neuroendocrine parameters and cyclic manic-depressive illness are also being explored.